WASHINGTON — The summer of 2010 was the foggiest on record in the Pacific Northwest, according to a researcher dubbed "Dr. Fog" by his colleagues.

Record levels of fog were reported in Seattle, Portland, Ore., Olympia, Wash., and from North Bend, Ore., to Quillayute, Wash., along the coast, said James Johnstone, a postdoctoral research associate at the University of Washington's Joint Institute for the Study of the Atmosphere and Oceans who's focused on West Coast fog.

Though the increase in fog is consistent with global warming computer models for the West Coast, Johnstone said there were other factors in play, with California actually becoming less foggy as the Northwest grew foggier.

"If there was an obvious connection to global warming, I would tell you," Johnstone said. "But we don't see any real strong evidence."

With fog on the decline in California there is increasing concern for the redwoods that hug a swath of the state's northern coast. Fog is considered a critical factor in the health of the giant trees and the rich ecosystem that has grown up around them.

"This system is finely tuned," said Todd Dawson, a biology professor at the University of California at Berkeley who's worked with Johnstone. "It's already been shown fog has an impact on the entire redwood ecosystem. Absolutely, this will be felt."

Dawson also said fog has been declining along the coast of Chile, Peru and West Africa.

The National Weather Service in Seattle doesn't track fog, and Johnny Burg, a weather service meteorologist, said he didn't have the "foggiest idea" whether 2010 was the foggiest on record in the Northwest.

Seattle-Tacoma International Airport had 29 days of heavy fog in 2010, compared with 41 normally, he said. But Olympia had 107 days of heavy fog last year, compared with 89 normally.

The difference between the weather service's tracking of foggy days and Johnstone's involves the definition of fog. The National Weather Services talks about heavy fog with a visibility of a quarter mile or less. Johnstone doesn't talk about heavy fog. Instead, he defines foggy as when the ceiling of clouds or fog is down to about 400 meters, or 1,300 feet.

"On the West Coast, it doesn't always hug the deck," he said.

Johnstone has spent years studying reports from various airports along the West Coast, especially smaller ones right along the coastline. At some of the airports, hourly readings of cloud heights date back 60 years.

In Quillayute, on the northern Washington coast, he found fog increased 7.4 percent since records were first kept in 1951 and at Astoria, on the Oregon side of the Columbia River, it was up 7.6 percent since 1966. At the same time, he found fog was actually decreasing on the California coast.

Under climate change computer models, warming temperatures inland were expected to produce more fog on the coast.

"But I don't think that model holds up," Johnstone said.

A high-pressure system usually parked off the West Coast during the summer typically has a major influence on the formation of coastal fog. Johnstone said the Pacific Decadal Oscillation, or PDO, a weather phenomenon in which every 30 years or so ocean water switches from warmer to colder and then back, was likely a key factor in fog formation.

The PDO has been in a cold phase since roughly 1998. During the prior PDO cold phase, 1945-76, there was also more fog reported along the coast.

"There are certain pieces that fit together and others that don't," Johnstone said. "I don't get the impression large-scale global warming is triggering this."

Cliff Mass, a professor of atmospheric sciences at the University of Washington, said he, too, thought the summer of 2010 was unusually foggy, but he leaves the details to Dr. Fog.

Mass dismisses any suggestion the foggy weather can be tied to climate change, calling it "extremely dangerous to point to one summer and say it is global warming."

Because of the way global warming is expected to spread unevenly around the globe, Mass said, the Northwest may well be one of the last places to feel its impact. He said the western Pacific is expected to warm faster than the eastern Pacific.

"The last place that will show major climate change impacts will be the eastern Pacific, he said. "Most of the global warming won't be seen here for 50 years or so."

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